1. Field of the invention
This invention relates in general to a mono-layer type or multi-layer type electrophotographic element, and in particular to a novel electrophotographic element having a photosensitive layer containing as an available ingredient a hydrazone compound having the following general formula (I) or an anile compound having the following general formula (II): ##STR3## [where R.sub.1 is a methyl, ethyl, 2-hydroxyethyl or 2-chloroethyl group; R.sub.2 is a methyl, ethyl, benzyl or phenyl group; and R.sub.3 is chlorine, bromine, a C.sub.1 -C.sub.4 alkyl group, a C.sub.1 -C.sub.4 alkoxy group, a dialkylamino group with C.sub.1 -C.sub.4 alkyl or a nitro group.] ##STR4## [where R.sub.1 is the same as the said general formula (I); and R.sub.4 is a substituted or non-substituted phenyl, naphthyl, heterocyclic or C.sub.1 -C.sub.10 alkyl group.]
As the substitution groups for the substituted phenyl referred to in the general formula (II) there can be enumerated C.sub.1 -C.sub.4 alkyl group, C.sub.1 -C.sub.4 alkoxy group, dialkylamino group with C.sub.1 -C.sub.4 alkyl, hydroxy group, etc. And, the heterocyclic group referred to in the general formula (II) includes pyridyl, benzothiazolyl and the like.
2. Description of the Prior Art
Inorganic substances such as selenium, cadmium sulfide, zinc oxide, etc. have hitherto been utilized as photoconductive materials for use in elements in electrophotographic processes. In this context, it is to be noted that the "electrophotographic process" referred to herein generally denotes one of the image forming methods which comprise the steps of electrifying a photoconductive element in the dark first of all for instance with corona discharge or the like, then exposing the element to light in an imagewise manner to selectively dissipate the charge from only the light struck portions of the element thereby forming a latent image and rendering the latent image visible by means of a developing process utilizing an electroscopic fine powder comprising a coloring agent called a toner such as dye, pigment or the like and a binder resin such as resin, high molecular substance or the like thereby forming a visible image. The element adapted for the above-mentioned electrophotographic process is required to possess the following fundamental characteristics: (1) capability of being charged with a suitable potential in the dark, (2) low discharge rate in the dark, (3) rapid dischargeability upon light radiation and so forth. The hitherto utilized inorganic substances as enumerated above surely possess a number of merits, but at the same time possess various demerits. For instance, the now universally utilized selenium can satisfy the aforesaid requirements (1) to (3) to a sufficient degree, but is defective in that it is manufactured with difficulty and consequently the manufacturing cost is high. In addition, the selenium is defective in that it is difficult to process the selenium, which has no flexibility, into a belt, close attention must be paid in handling the selenium which is very sensitive to mechanical impacts and the like. On the other hand, the cadmium sulfide and zinc oxide are utilized in the element in the manner of their being dispersed in a binder resin. However, such element lacks the mechanical characteristics such as smoothness, hardness, tensile strength, frictional resistance, and therefore it can not stand repeated use.
In recent years, electrophotographic elements employing various kinds of organic substances have been proposed in order to remove the drawbacks inherent in the inorganic substances as enumerated above. Some of said elements are put to practical use, for instance, such as the element including poly-N-vinylcarbazole and 2,4,7-trinitrofluorene (U.S. Pat. No. 3,484,237), the element including poly-N-vinylcarbazole sensitized with a pyrylium salt type pigment (Japanese Patent Publication No. 25658/1973), the element including an organic pigment as the principal ingredient (Japanese Laid-open Patent Application No. 37543/1972), the element including a cocrystalline complex consisting of dye and resin as the principal ingredient (Japanese Laid-open Patent Application No. 10735/1972), etc. However, the fact is that these elements surely are considered to possess superior characteristics as well as high practical values, but, when taking into consideration various requirements for elements, can not meet these requirements yet to a satisfactory degree.
On the other hand, it is perceived that these excellent elements, though there is a difference therebetween depending on their objects or manufacturing processes, can generally exhibit superior characteristics as a result of incorporating high-efficient photoconductive materials therein.